The Relationship Between Polymorphism of The Prolactin Gene and The Production of Milk, its Components, and The Reproductive Performance of Holstein Cows

The study was conducted at the Al-Khalis dairy production station in Diyala Governorate during the 2021-22 production season on 63 Holstein cows to determine the effect of polymorphism of the prolactin gene (PRL) on their milk production, its components, and their reproductive traits. The results showed that the three TT, TC, and CC genotypes had highly significant different ratios at 77.78%, 19.05%, and 3.17%, respectively. The frequency of the T and C alleles was 0.87 and 0.13, respectively. Total milk yield was significantly higher in the TC genotype at 4398.00 kg followed by the TT and CC genotypes at 3957.98 kg and 3505.00 kg, respectively. The polymorphism of PRL had a significant effect on milk composition but did not affect the reproductive traits of the cows. Therefore, the selection of hybrid individuals according to the prolactin gene will help increase milk production, and economic returns, and can thus be used for improving the genetics of dairy cows